CAMBRIDGE ‚ÄĒ A scene of chaos descended on Cambridge and Watertown late Thursday night and early Friday morning, as police confirmed an MIT police officer was shot and killed, and an apparent carjacking led police on a wild chase into Watertown.

Dozens of police officers descended on Watertown Square after midnight. Separately, MIT‚Äôs website reported just after 1 a.m. the suspect in the university officer‚Äôs shooting remained at large.

FBI agents were on the scene in Watertown. ‚ÄúThis is still extremely dangerous,‚ÄĚ an FBI agent said.

A man in handcuffs was being questioned by the FBI in the back of an ambulance.

At Arsenal Court and Arsenal Street in Watertown, an officer bellowed: ‚ÄúYa gotta get outta here. There‚Äôs an active shooter here with an active explosive. Go!‚ÄĚ

Police were demanding that cellphones be turned off.

The officer, who has not been identified, was shot multiple times at 10:48 p.m., according to the Middlesex district attorney‚Äôs office. No one else was hurt, and no *arrests had been made by early Friday.

The manhunt fanned out from *Kendall Square over an area that has endured a tragic and tumultuous week, in the aftermath of the fatal explosions at Monday‚Äôs Boston Marathon. There was no report of a connection between the two events, but the swarm of sirens and circling helicopters rattled a region already on edge.

Police from several agencies were conducting a manhunt for the gunman across the school campus and on the T‚Äôs Red Line, according to authorities.

MIT and Cambridge police responded to a report of shots fired at 10:48 p.m. Thursday near Main and Vassar streets, according to the university.

Police officers and canine units swept the campus, and a big swath of Vassar Street was blocked.

The university issued an alert to students and faculty to remain inside.

An eerie quiet descended on the campus as teams of *police officers combed the campus block by block. SWAT teams were present.

Police checked bushes and alleys and yanked on doors.

Officers from the MIT and Harvard departments, as well as Cambridge and State Police, were present.

Siddhartha Varshney was walking home from dinner with two friends when they were stopped at the police cordon.

‚ÄúInitially, we thought they had caught the suspect in the bombing,‚ÄĚ the 28-year-old said. But they then learned it was a shooting involving an MIT officer.

‚ÄúWell, I ‚ÄĒ honestly ‚ÄĒ I mean, I can‚Äôt think what I make of it. The situation is a little tense,‚ÄĚ he said. ‚ÄúAnd I hope that whoever he is gets caught.‚ÄĚ

Few seemed to be out on the campus at the time of the shooting. One professor, standing feet from the police tape, said he came out of his office when he heard a commotion of sirens and saw *police lights.

At around midnight, a frantic scene was unfolding at Massachusetts General Hospital, where a dozen police cars arrived with sirens on and several women were brought in by police, looking deeply *upset.

A police patrol boat could be seen cruising the Charles River, though it did not *appear that an intensive search was occurring on the water.

So, is this stuff related to the MIT shooting, the Marathon bombing, or something completely unrelated? Anything actually known about it yet? Were police following a lead on something or was it an entirely new incident?